The design of the repository for high-level nuclear waste (HLW) in France consists of a multiple-barrier system including steel canisters in a clay host rock. The system will undergo temperature variations in time and space, the heat source being the HLW within the canisters. The effect of a thermal gradient in space on the Fe-claystone interaction was investigated here by applying a thermal gradient (150–300°C and 80–150°C) to a mix of claystone, Fe, and an aqueous chloride solution over periods of 3 and 6 months. Following the reaction, the starting clay minerals (mostly illite and mixed-layer illite-smectite) evolved toward chlorite, Fe-serpentine, Fe-saponite, mixed-layer chlorite-smectite, or mixed-layer serpentine-smectite as a function of temperature. Iron corrosion made the medium basic and reductive. Magnesium enrichment of clay minerals was observed in the hottest part of the experiment due to Mg migration under the thermal gradient. Reaction progress was enhanced at the lowest temperatures, compared to batch experiments.

During several hundred years of burial in the soil, glass objects, especially those with the high potassium content of medieval compositions, develop heavily corroded surfaces, showing phenomena such as local pitting, laminated layers, and browning effects. The long-term behavior of glass in the soil or in contact with groundwater is not only of interest to glass scientists with a background in archaeology, but also for those with a special interest in nuclear-waste management. Several attempts have been made to propose the decomposition of ancient glasses as an indicator for the performance of buried nuclear-waste glasses. In spite of differences in glass composition and exposure conditions, the development of alteration or corrosion layers with time is a common concern, as shown in this article. Laboratory experiments, representing a simplified model for real conditions, offer the possibility for systematic investigations.